This investigation extends the experimental model previously designed to quantitate the biologic and physical aspects of repair in canine segmental fibular cortical bone grafts. Utilizing the model, studies will be conducted to determine the repair in bilateral autografts, bilateral grafts in which one is an allograft, and the effect of Imuran on the repair for both types of grafts. It is anticipated from the pilot study and reports on Imuran as an immunosuppressant that bone allografts will mimic autografts in physical and biologic terms. The amount and spatial configuration of repair will be quantitated by continuous tetracycline labeling, microradiography, radiography, and torsional loading to failure. The data will provide guides as to the relation between the stresses exerted on autogenous and allogeneic cortical bone grafts and the mechanical and/or biologic failure of such grafts. Finally data on human bone grafts will be continually collected on an available and appropriate basis with the attempt to correlate the results to that found on an experimental basis.